Accurate needle placement is essential in percutaneous procedures such as radiofrequency ablation (RFA) of liver tumors. Use of real-time navigation of an interventional needle can improve targeting accuracy and yield precise measurements of the needle tip inside the body. An emerging technology based on Fiber Bragg Grating (FBG) sensors has demonstrated the potential of estimating shapes at high frequencies (up to 20 kHz), fast enough for real-time applications. In this paper, we present a calibration procedure for this novel needle tracking technology using strain measurements obtained from fiber Bragg gratings (FBGs). Three glass fibers equipped with two FBGs each were incorporated into a 19G needle. The 3D needle shape is reconstructed based on a polynomial fitting of strain measurements obtained from the fibers. The real-time information provided by the needle tip position and shape allows tracking of the needle deflections during tissue insertion. An experimental setup was designed to yield a calibration that is insensitive to ambient temperature fluctuations and robust to slight external disturbances. We compare the shape of the 3D reconstructed needle to measurements obtained from camera images, as well as assess needle tip tracking accuracy on a ground-truth phantom. Initial results show that the tracking errors for the needle tip are under 1mm, while 3D shape deflections are minimal near the needle tip. The accuracy is appropriate for applications such as RFA of liver tumors.
The coordination of a fleet of miniature instrumented wireless robots operating within a half-meter diameter surface area requires a special infrastructure. The infrastructure described in this paper allows an excess of 100 of these robots to operate simultaneously and continuously at the atomic scale. Among many tasks, the infrastructure provides 4 Mb/s half-duplex infrared communication with all robots. It also provides an infrared positioning system based on a position sensing detection technique capable of positioning each robot within the whole workspace to +/- 1.585 mm. The positioning and angular information is also used by the infrastructure to control the displacements of all robots by communicating proper information and instructions to ensure that each robot reaches its assigned destination with minimum delay and without problems. While tracking the position and the status of each robot, a graphical user interface is also provided and updated, allowing user interactions. The infrastructure also includes a special power supply distribution scheme, a high precision walking and working surface, and electronics and software for the real-time automatic management of the nano-robotic platform.
Implementing instruments in the form of wireless miniature robots designed to operate at the atomic scale requires a positioning system capable of atomic resolution over a relatively large surface area. Interferometers or similar instruments are not adequate for such an environment because of the high probability that another robot obstructs the path of the laser during position measurement. As such, we have developed an infrared system based on a position sensing detection technique mounted on an x-y stepping stage where the position of an infrared signal transmitted upward from a miniature wireless robot can be detected with a resolution of +/- 1.585 micrometers over a 0.5 meter diameter circular surface. Although a fleet of miniature robots distributed over a relatively large area can be supported simultaneously, the system is still far from reaching positioning accuracy down to the level of a single atom. This is why we are embedding the capability to detect surface features down to the size of a single atom using scanning tunneling microscopy (STM) techniques onto the miniature robots. The dynamic range of the scanning piezo-tube is one of many design issues that must be carefully planned. For instance, the scanning system must be capable of detecting each atom in the scan path in order to determine the distance by counting the number of atoms while the maximum scan range must reach the discrimination level of the infrared positioning system despite many artifacts such as non-linearity errors and hysteresis. The feasibility and the design of such system are described.
The Telemetric Electrode Array System (TEAS) is a surgically implantable device for the study of neural activity in the brain. An 8x8 array of electrodes collects intra-cortical neural signals and connects them to an analog front end. The front end amplifies and digitizes these microvolt-level signals with 12 bits of resolution and at 31KHz per channel. Peak detection is used to extract the information carrying features of these signals, which are transmitted over a Bluetooth-based radio link at 725 Kbit/sec. The electrode array is made up of 1mm tall, 60-micron square electrodes spaced 500 microns tip-to-tip. A flex circuit connector provides mechanical isolation between the brain and the electronics, which are mounted to the cranium. Power consumption and management is a critical aspect of the design. The entire system must operate off a surgically implantable battery. With this power source, the system must provide the functionality of a wireless, 64-channel oscilloscope for several hours. The system also provides a low-power sleep mode during which the battery can be inductively charged. Power dissipation and biocompatibility issues also affect the design of the electronics for the probe. The electronics system must fit between the skull and the skin of the test subject. Thus, circuit miniaturization and microassembly techniques are essential to construct the probe's electronics.
Bringing instruments capable of atomic scale operations in the form of miniature wireless robots yields very high-density powered electronics. As the robots are further miniaturized, the surface area available for heat dissipation becomes inadequate to maintain continuous operation of the onboard electronics. Typical approaches such as increasing the surface area by mounting a heat sink is not an option since it would increase substantially the overall size of the robot. The overall size has to be minimized to allow a larger fleet of miniature robots to operate simultaneously in the same area. A larger fleet translates to higher throughput for mass-scale atomic-level operations. To solve this issue, we have implemented a special skin in contact with the high-powered flexible electronic circuit surrounding the robot's body. The skin effectively dissipate heat by evaporating distilled water stored in a few layers of flexible patterned wiping fabric designed for maximum water absorption and encapsulated between an inner thin layer of thermally conductive elastometer and an outer thin layer of an heat conducting metal sheet. Without the skin, past experiments have shown that each robot would operate for approximately 10 seconds before shutting down. With a 1-mm thick skin on a 32-mm diameter size robot, experimental results have shown that each robot could operate up to approximately 5 minutes between refills. A thicker water absorption layer is not a valid option since it would increase the overall size of the robot. A refill methodology suitable for this environment is also described.
Amplitude modulated piezo-based locomotion requires one power amplifier for each quadrant electrode on the piezo-legs of miniature robots. Since each amplifier has a significant amount of quiescent current, several DC/DC converters must be embedded to source at least the total amount of quiescent current. In order to achieve a significant reduction in the overall size of the piezo-actuated robots, the number of DC/DC converters is reduced through frequency modulation. Using frequency modulation, the amplitudes of deflection or the step sizes are reduced by modulating the piezo-legs above the resonant frequency. Although the frequency modulated approach can result in much smaller robots than what can be achieved using the amplitude modulated technique, it has some drawbacks that the amplitude modulated approach does not have. First, the magnitudes of deflection of the piezo-legs using frequency modulation are typically more difficult to control. Secondly, for much smaller amplitudes of deflection, the onboard electronics must operate faster, yielding an increase in power consumption and an increase in temperature of the miniature robot, which in turn may affect sensitive embedded instruments. Furthermore, modulating the piezo-legs above the resonant frequency yields a reduction in efficiency, which translates into additional heat. When very small deflections are required, the risk of the temperature to rise beyond the Curie temperature of the piezo-material may also become an issue. All these factors must be considered carefully when frequency modulated piezo-based locomotion is used.
Sylvain Martel, Lorenzo Cervera Olague, Juan Bautista Coves Ferrando, Stefen Riebel, Torsten Koker, Jeremy Suurkivi, Timothy Fofonoff, Mark Sherwood, Robert Dyer, Ian Hunter
The NanoWalker is a miniature wireless instrumented robot designed for high-speed autonomous operations down to the atomic scale. As such, it requires very advanced electro-mechanical specifications and complex embedded sub-systems. The locomotion is based on three piezo-ceramic legs that are modulated at high frequencies to achieve several thousand steps per second with computer-controlled step sizes ranging from a few tenths of nanometers to a few micrometers. Each robot has an onboard 48 MIPS computer based on a digital signal processor (DSP) and 4 Mb/s half-duplex infrared communication system. A special instrument interface has been embedded in order to allow positioning capability at the atomic scale and sub-atomic operations within a 200 nanometer surface area using a scanning tunneling microscope (STM) tip. The design allows 200,000 STM-based measurements per second. In this paper, we describe the many sub-systems and the approaches used to successfully integrate them onto such a miniature robot.
Piezo-actuators due to their relatively high resonant frequencies and small deflections are ideally suited as accurate displacement transducers. As such, they have been used to implement the legs of the miniature wireless NanoWalker robot where step sizes in the order of a few tenths of nanometers are required for final positioning within the range of an embedded instrument designed to operate at the atomic scale. The relatively high capacitance combined with the high-drive voltage requirement of the actuators, impose constraints on the miniaturization of the electronics. The amplitude modulation scheme requires one amplifier per quadrant electrode on the piezo-legs. Although power amplifiers are suited to drive large capacitive loads with large signal amplitudes without stability problems, the quiescent current of the amplifiers requires several DC/DC converters of significant size. During locomotion, the sudden current increase occurring when high slew rate signals are used during the charging/discharging cycle of the capacitive loads at each walking step, causes the power rail voltage to drop, yielding a reduction in the amplitude of the deflections of the piezo-legs. To minimize the number of DC/DC converters, the slew rate requirement of the drive signal is reduced by an increase of the angular acceleration of the leg created by an initial static friction force with the walking surface. It is then suggested that further miniaturization of the embedded electronics can be achieved by adjusting the kinematic behavior of the piezo-legs with an appropriate mechanical design and the right friction coefficient through careful materials selection.
The development of a three-legged miniature robot, such as the NanoWalker, capable of taking steps in the micrometer and sub-micrometer range and equipped with instruments such as scanning, tunneling microsope (STM) tip, requires an adequate positioning system. In order to make use of these instruments, positioning the robot becomes one of the most critical issues. For atomic scale operations within a relatively large workspace, no traditional positioning systems were adequate for this type of robotic environment. The proposed atomic scale positioning system relies on three positioning levels where at each level, the resolution improves from 10 micrometers down to a few picometers while the circular positioning area decreases from 0,5 meter down to 200 nanometers in diameter. While the last two levels are STM- based positioning techniques, the first level with the largest positioning area is based on optical techniques. The paper describes the final set-up for implementing the first positioning level that incorporates a lateral effect photodiode to make measurements of the robot's position by detecting infrared signals emitted by the robot. Using a lens to project the robot's workspace onto the photodiode we are able to achieve of a resolution of a few micrometers in the central region of a typical 0.5-meter workspace. Due mainly to loss of signal at the edges of the workspace,the resolution of the system decreases as we near the edges.
The NanoWalker is a miniature autonomous wireless robot under development. The robot is designed to accomplish complex tasks at the molecular and atomic scales. One concern is the total mass of the robot. With all the components including the mechanical structure and the complex electronic system necessary to embed the required functionality of throughput for such tasks, the mass of such a robot is estimated to be in the range of 100-200 grams depending on tradeoffs in the final design. With such a mass and limitations on the maximum voltage and current outputs that can be generated in a small form factor to deflect the piezo-ceramic legs with high-precision, a preliminary evaluation and experimentation phase of the motion behavior is essential prior to completing the final desing. It is shown both theoretically and experimentally that adequate motions are possible under such high normal forces. This was achieved through a new walking strategy referred to here as the push-slip method. The method uses the high normal forces combined with the resulting coefficient of friction between the termination of each leg and the walking surface to create initial opposite forces to the bending forces of each leg. These opposite forces, bounded by the maximum static force of friction, can be used for pushing or slipping through additional torque if the bending forces are applied reciprocal or in the direction of intended motions respectively. With the right parameters combined with tight and proper synchronizations of the legs, very effective motions can be achieved.
The NanoRunner is designed to be primarily used as an experimental wireless robot in order ot quickly test and validate several hardware/software issues and ideas prior to being implemented on the more expensive and complex wireless instrumented NanoWalker robot. As such, the NanoRunner, Like the NanoWalker is based on three piezo- actuated legs forming a pyramid with the apex pointing upward. Unlike the NanoWlaker, the NanoRunner has much simpler embedded electronics and is not capable of an accuracy and computational throughput comparable to the NanoWalker. Because of its lighter weight, it can move or run much faster. Furthermore, the NanoRunner does not have a fast infrared communication infrastructure for downloading executable code. Instead the NanoRunner is first pre-programmed with a specific behavior suitable for the tasks to be performed. Nonetheless, the NanoRunner has all the required electronics to be fully autonomous while performing its experimentation tasks. Although not as sophisticated as the NanoWalker, the NanoRunner offers a smaller and simpler robot implementation for less demanding tasks. Another major motivation for the NanoRunner is to validate various ideas in order to decrease the overall size of the robot. The size is critical since our goal is to allow more robots to work within the same area. In this paper, the NanoRunner is described. Aspects such as construction, assembly, and the method used for downloading executable code in order to pre-program the robot's behavior are also covered.
It is well known that one of the major limitations in achieving small form factors in wireless electronic systems is the power source. This particularly holds true for a new class of miniature wireless robots such as the NanoWalker where complex and power-demanding electronics and computation must be embedded to support complex tasks at the molecular and atomic scales while providing very high throughputs in a fully autonomous manner. It is estimated that in a worst case, up to 15 Watts of continuous power may be required per robot. This power consumption comes mainly from the embedded 48 MIPS digital signal processing (DPS) and memory system, the drive and control electronics for the piezo- ceramic legs, the scanning tunneling microscope (STM) based control and instrumentation sub-system capable of 200,000 high-resolution readings/s, and the 4 Mb/s infrared (IR) communication interface. With these specifications coupled with the requirement to control the motion of the robot in the nanometer and micrometer ranges with several thousand steps/s, migrating some of the control functions to an external computer and exchanging data through the wireless communication channel is not an option because of additional latencies well beyond the short and highly predictable response periods required by the robots. To complicate the problem, the power delivery system must accommodate a large range of voltages between the electronics and the power amplifiers driving the piezo-ceramic legs. A solution based on continuous power delivery through a special walking surface with intermittent contacts with the robots during motion is described.
The NanoWalker project aims at developing a new type of miniature wireless autonomous robot capable of performing tasks at the molecular and atomic scales. To do so, the robot must be capable to position itself within the maximum range of the embedded instrument by using a new type of relatively fast locomotion system capable of sub-micrometer step sizes. To prevent excessive traveling delays due to the critical requirement of small step sizes, relatively fast motions have been achieved through several thousand steps executed per second and operation at resonance frequency. Furthermore, step sizes larger than the maximum bending amplitude of the piezo-legs have been achieved with jumps initiated by extremely fast onboard computer controlled angular accelerations of the legs form known parameters such as mass, moment of inertia, and coefficient of friction, just to name a few. This locomotion system is based on three piezo-actuated legs formed as a pyramid with the apex pointing upward. Although this structure is relatively simple, its kinematic behavior becomes extremely sensitive to many variables that must be well understood. Such understanding is critical for the embedded computer system responsible for controlling the three legs. In this paper, an introduction with the fundamental principles behind this new actuation system is presented.
KEYWORDS: Amplifiers, Scanning tunneling microscopy, Electrodes, Wireless communications, Control systems, Analog electronics, Signal processing, Digital signal processing, Human-machine interfaces, Telecommunications
The aim of this project is to develop the smallest and most sophisticated wireless fully autonomous instrumented robot capable of subatomic movements. The robot named 'NanoWalker' should bring a new paradigm in the way instruments are built while providing a sophisticated platform for a new range of applications. The project involves primarily the investigation of a new legged locomotion based on piezo-actuators with advanced micro-assembly techniques applied to complex embedded electronic systems; the development of new miniature instruments, micro-manipulators, integrated behavior for controlling, searching and scanning at the atomic scale; and the development of a subatomic navigation system. Besides all the new technologies and techniques that we intend to develop and which will be applicable to many areas and systems, the NanoWalker should provide a suitable yet more flexible and powerful platform compared to traditional macro-scaled instruments. It is anticipated that this new form of highly integrated autonomous microsystem will be used as the main building block for a new generation of measurement and inspection systems. In this paper, the main components of the NanoWalker are briefly described.
The integration of complex electronic systems onto small- scale robots requires advanced assembly methods. The NanoWalker is an example of such a robot where a large amount of electronics must be embedded in the smallest possible space. To make a space-efficient implementation, electronic chips are mounted using flip chip technology on a pre-bumped flexible printed circuit (FPC). A 3D structure is obtained by mounting the FPC vertically in a triangular fashion above a tripod built with three small piezo-actuated legs used for the walking and rotational motions. Advanced computer aided design systems are used for the design and to generate manufacturing files. Unlike other commercial products such as cellular phones, watches, pagers, cameras, and disk drives that use flip chip technology to achieve the smallest form factor, the assembly process of the NanoWalker is directly dependent on other characteristics of the system. Minimization of coupling noises through proper FPC layout and die placement within temperature constraints due to the proximity of sensitive instrument was a critical factor. The effect of vibration caused by the piezo- actuators and the weight of each die were also other important issues to consider to determine the final placement in order to maintain proper sub-atomic motion behavior.
The NanoWalker project is an attempt to explore a new approach in the development of various instruments. The idea is to build a small autonomous robot capable of nanometer range motions that will provide a standard platform for new miniaturized embedded instruments. This modular approach will allow easy expansion in instrumentation capability through the use of an arbitrary number of NanoWalkers which would perform similar or different measurement simultaneously on various samples. To do so, a fair amount of electronics must be embedded for infrared wireless communication, processing, support for the embedded instrument, and accurate control and drive capability for the piezo-actuated motion system. Miniaturization of the whole assembly is also a key characteristic to allow more robots to operate simultaneously within smaller surface areas. As such, new assembly techniques applicable to small volume production must be used to achieve the smallest possible implementation. The integration phase within the technological constraints is complicated by the fact that several factors such as the weight and weight distribution of the electronic assembly will have a direct impact on the very sensitive motion behavior of the robot. The NanoWalker is briefly described with the integration phases and the requirements that must be met by the assembly process.
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